The Linaceae comprise about 150 species of herbaceous plants and shrubs within 14 genera which provide fibre and oils (e.g. Linum usitatissimum L., flax). The fruits are usually capsules, but sometimes drupes. The seeds show orthodox storage behaviour.
SEED DORMANCY AND GERMINATION
The seeds can show considerable dormancy. B.R. Atwater classifies seed morphology as non-endospermic seeds with axile foliar embryos within thin, mucilaginous seed coats (see Table 17.2, Chapter 17). Potassium nitrate, low germination test temperatures, alternating temperatures, and pre-chilling are generally promotory treatments. Detailed information is provided in this chapter for the genus Linum only, but the algorithm below may be helpful in developing suitable germination test procedures for difficult accessions of Linum and other species.
RBG Kew Wakehurst Place algorithm
The first step in the algorithm is to test the seeds at constant temperatures of 16°C, 21°C and 26°C with light applied for 12h/d. If full germination has not been achieved and the results of these tests indicate a trend in the response of germination to constant temperatures then test a further sample of seeds at a more extreme constant temperature. For example, if the greatest proportion of seeds germinates at 16°C, then test a further sample of seeds at a constant temperature of 11°C with light applied for 12h/d.
If the first step of the algorithm has not resulted in full germination then the second step is to test a fresh sample of seeds in an alternating temperature regime of 23°/9°C (12h/12h) with light applied for 12h/d during the period spent at the upper temperature.
If the second step of the algorithm has not resulted in full germination then the third step is to co-apply 7 x 10-4 M GA3 to the germination test substrate and test a fresh sample of seeds in the most appropriate temperature regime determined from the results of steps one and two.
If the third step of the algorithm has not resulted in full germination then the fourth step of the algorithm is to pre-chill a fresh sample of seeds at 2° to 6°C for 8w and then test in the most appropriate regime determined from the results of steps one to three. This may include a GA3 treatment if a comparison of the results of step three with those of steps one and two indicate that the GA3 treatment is promotory.
LINUM
|
L. flavum L. |
golden flax |
|
L. grandiflorum Desf. |
flowering flax |
|
L. narbonense L. |
|
|
L. perenne L. |
perennial flax |
|
L. usitatissimum L. |
flax |
I. Evidence of dormancy
Freshly harvested seeds of L. usitatissimum can be dormant (5,6), and after-ripening for 3-4 (6) or 6 (5) months is required to remove this dormancy.
II. Germination regimes for non-dormant seeds
L. flavum
TP; BP: 20°/30°C (16h/8h); 15°C; 20°C: 21d (ISTA)
TP: 20°/30°C (16h/8h): 18d (AOSA)
Constant temperatures: 20°C, 21d (1)
L. grandiflorum
BP; TP: 15°C; 10°C; 20°C: 21d (ISTA)
TP: 15°C: 12d (AOSA)
Constant temperatures: 15°C, 14d (1)
L. narbonense
TP; BP: 20°/30°C (16h/8h); 15°C; 20°C: 21d (ISTA)
L. perenne
BP; TP: 15°C; 10°C; 20°C: 21d (ISTA)
TP: 15°C: 14d (AOSA)
Constant temperatures: 15°C, 21d (1)
L. usitatissimum
BP; TP: 20°/30°C (16h/8h); 20°C: 7d (ISTA)
BP, S: 20°/30°C (16h/8h): 7d (AOSA)
Constant temperatures: 15°C (8); 20°C (3,5); 22°-25°C (7); 28°C in dark (10); 30°C (4,14)
Alternating temperatures: 15°/31°C (12h/12h) (15); 20°/30°C, 25°/35°C (18h/6h) (4); 20°/30°C (16h/8h) (3,4,9,13)
III. Unsuccessful dormancy-breaking treatments
L. usitatissimum
Constant temperatures: 1°C, 40°C (12)
Alternating temperatures: 25°/40°C, 40°/20°C, 40°/25°C (18h/6h) (4)
Pre-dry: 40°C, 50°C, 65°C, 1h (15)
Deuterium oxide: co-applied, 25-100% (1)
Boric acid: co-applied, 10-4, 10-2 M (10)
Sodium metaborate: co-applied, 10-4, 10-2 M (10)
Sodium tetraborate: co-applied, 10-4, 10-2 M (10)
IV. Partly-successful dormancy-breaking treatments
L. perenne
Constant temperatures: 15°C, 25°C, 30°C, in light, 155x10-6 mol m-2 s-1 (11)
L. usitatissimum
Alternating temperatures: 20°/30°C (16h/8h) (9)
Pre-chill: 10°C, 4d, germinate at 20°C (5)
Potassium nitrate: co-applied, 0.2%, plus pre-chill, 10°C, 4d, germinate at 20°C (5)
Boric acid: co-applied, 10-6 M (10)
Sodium metaborate: co-applied, 10-6 M (10)
Sodium tetraborate: co-applied, 10-6 M (40)
V. Successful dormancy-breaking treatments
L. flavum, L. grandiflora
Potassium nitrate (AOSA, ISTA)
L. narbonense
Potassium nitrate (ISTA)
L. perenne
Potassium nitrate (AOSA, ISTA)
Constant temperatures: 20°C, in light, 155 x 10-6 mol m-2 s-1 (11)
L. usitatissimum
Pre-chill (ISTA)
Constant temperatures: 5°C, 15°C, 25°C, in dark (8); 4°C, 14°C, 16°C (16)
Pre-chill: 5°C, 5d, germinate at 20°/30°C (16h/8h) (9)
VI. Comment
The optimum range of constant temperatures for the germination of seeds of L. usitatissimum is 4° to 20°C (8,16). Pre-chilling (9) or pre-chilling plus co-applied potassium nitrate (5) are very effective dormancy-breaking treatments. It is suggested that the ISTA rules are satisfactory for germination but it may prove worthwhile to investigate whether the pre-chill regime should be extended and considered as the germination test regime - rather than subsequently transferring to a higher temperature.
VII. References
1. Atwater, B.R. (1980). Germination, dormancy and morphology of the seeds of herbaceous ornamental plants. Seed Science and Technology, 8, 523-573.
2. Blake, M.I., Crane, F.A., Uphaus, R.A. and Katz, J.J. (1968). Effect of heavy water on the germination of a number of species of seeds. Planta, 78, 35-38.
3. Decker, A.E. and Reitz, L.P. (1948). Germination tests with flax stored at different moisture and temperature levels. Proceedings of the International Seed Testing Association, 14, 27-34.
4. Dillman, A.C. and Toole, E.H. (1937). Effect of age, condition, and temperature on the germination of flax seed. Journal of the American Society of Agronomy, 29, 23-29.
5. Doyle, E.J., Robertson, E. and Lewis, N.G. (1952). The effect of potassium nitrate on the germination of freshly harvested wheat, oats, barley and flax seed. Proceedings of the Association of Official Seed Analysts, 42, 93-101.
6. Frederiksen, P.S. (1955). [Germination tardiness of fibre-flax seed.] Lin, 9, 85-87. (From Field Crops Abstracts, 1957, 10, 248.)
7. Gupta, D. and Basak, S.L. (1983). Genetics of germination and seedling growth of flax (Linum usitatissimum). Seed Science and Technology, 11, 251-256.
8. Harper, J.L. and Obeid, M. (1967). Influence of seed size and depth of sowing on establishment and growth of varieties of fiber and oil seed flax. Crop Science, 7, 527-532.
9. Higgins, E.C. (1951). Flax germination - crops of 1950. Proceedings of the Association of Official Seed Analysts, 41, 88-89.
10. Jensen, W. (1951). Effect of boron on germination of flax seed and on respiration of flax seedlings. Botanical Gazette, 113, 180-185.
11. Kaspar, M.J. and McWilliams, E.L. (1982). Effects of temperature on the germination of selected wild flower seeds. HortScience, 17, 595-596.
12. Mandy, G.Y., Szabo, L. and Papp, E. (1971). [Examination of cardinal points of germination in poppy and flax varieties.] Agrobotanika, 11, 169-174. (From Field Crop Abstracts, 1973, 26, 1912.)
13. Reitz, C.P. Hansing, E.D., Davidson, F.E. and Decker, A.E. (1947). Viability and seed treatment of flax. Journal of the American Society of Agronomy, 39, 959-970.
14. Salehuzzaman, M. and Pasha, M.K. (1979). Effects of high and low temperatures on the germination of seeds of flax and sesame. Indian Journal of Agricultural Sciences, 49, 260-261.
15. Siegel, S.M. (1950). Effects of exposures of seeds to various physical agents. 1. Effects of brief exposures to heat and cold on germination and light sensitivity. Botanical Gazette, 112, 57-70.
16. Trifonov, N.P. (1980). [Temperature and germination of flax seed.] Len i Kinoplya, 1, 26-27. (From Field Crop Abstracts, 1981, 34, 10443.)
